1. Field of the Invention
The present invention relates generally to a communication terminal, and in particular, to an apparatus and method for correctly sensing a state of a 4-pole earmicrophone in a communication terminal.
2. Description of the Related Art
Commonly, a portable terminal uses a 3-pole earmicrophone or a 4-pole earmicrophone. The 4-pole earmicrophone is connected to a communication terminal with a 4-pole jack including two receiver terminals and two common terminals for both a microphone (MIC) and a switch.
FIG. 1 illustrates a structure of a 4-pole earmicrophone jack. As illustrated in FIG. 1, the jack includes four terminals, i.e., two receiver terminals and two common terminals for a microphone and a switch.
Circuit operations according to earmicrophone states will be described below with reference to FIGS. 2 to 5.
FIG. 2 is a circuit diagram of a jack connector by which the earmicrophone is connected to a communication terminal. FIG. 3 is an equivalent circuit diagram of the jack connector when an earmicrophone is not connected. FIG. 4 is an equivalent circuit diagram of the jack connector when an earmicrophone is connected. FIG. 5 is an equivalent circuit diagram of the jack connector when a switch is turned on with an earmicrophone connected.
Basically, the jack connector is configured to sense an earmicrophone jack connection by its mechanical connection to an earmicrophone jack, and a switch-on of the earmicrophone as illustrated in FIG. 2. Upon detection of the jack connection, the jack connection outputs a high signal through a jack detection terminal, and upon detection of the switch-on, the jack connection outputs a high signal through a switch detection terminal.
A description will first be made of an equivalent circuit of the jack connector illustrated in FIG. 2 when the earmicrophone is not connected, which is illustrated in FIG. 3. Referring to FIG. 3, when the earmicrophone is disconnected in FIG. 2, audio signals are exchanged between a microphone, a receiver and a voice processor such as a DSP (Digital Signal Processor) in the communication terminal. Here, the audio signals pass through terminals 1, 2, 5 and 6 in FIG. 2. A voltage 0.21V (=VCC×(R3/R1+R2+R3)=0.07×3V) is applied between a second resistor with a resistance R2 and a third resistor with a resistance R3. As a result, no currents flow through the bases of first and second transistors TR1 and TR2 and thus the first and second transistors TR1 and TR2 do not turn on. Consequently, the jack detection terminal and the switch detection terminal output low signals to a controller in the communication terminal (not shown). The controller senses earmicrophone disconnection and switch-off by the detection signals.
Referring to an equivalent circuit of the jack connector illustrated in FIG. 2 during an earmicrophone connection, i.e., if the earmicrophone is inserted into the communication terminal, a mechanical contact terminal detaches a terminal 3 from the terminal 2 and the terminal 5 from a terminal 4. Instead, the microphone and receiver of the earmicrophone are connected to the terminals 1, 2, 5 and 6. Therefore, audio signals are exchanged between the microphone and receiver of the earmicrophone and the voice processor of the communication terminal via the terminals 1, 25 and 6, with the microphone and receiver of the communication terminal disabled.
Referring to FIG. 4, the resistance between the base of the first transistor TR1 and a power supply for supplying a power voltage VCC is 16.5KΩ(=R1+R2+R4). As a result, the first transistor TR1 is turned on and thus a high signal is output through the jack detection terminal. Meanwhile, a voltage of 0.21V (=VCC×(R3/(R1+R10+R3))=0.7×3V) is applied between a resistor R10 with a resistance of 6K and the third resistor R3, no current flows through the base of the second transistor TR2. That is, the second transistor TR2 is disabled and thus a low signal is output through the switch detection terminal. Therefore, the controller of the communication terminal senses an earmicrophone connection and a switch-off by the high jack detection signal and the low switch detection signal.
FIG. 5, is an equivalent circuit of the jack connector illustrated in FIG. 2 during an earmicrophone connection and a switch-on, since the first resistor R1, second resistor R2 and fourth resistor R4 with the resistances 500, 6K and 10K (16.5KΩ(=R1+R2+R4) in total) are connected between the base of the first transistor TR1 and the power supply, the first transistor TR1 is turned on and a high signal is output through the jack detection terminal. A voltage of 1.5V (=VCC×(R3/(R1+R3)=0.5×3V) is applied between the first and third resistors R1 and R3, and current flows through the base of the second transistor TR2. That is, the transistor TR2 is turned on and a high signal is output through the switch detection terminal. Therefore, the controller of the communication terminal senses a switch-on with the earmicrophone connected by the two high detection signals.
The jack connector illustrated in FIGS. 2 to 5 corresponds to a microphone circuit connected to the microphone of the communication terminal. In other words, a communication terminal using a 4-pole earmicrophone senses earmicrophone states by setting a different voltage difference for each earmicrophone state using the bias voltage of the microphone circuit.
Table 1 and Table 2 below define earmicrophone states depending on jack detection signals and switch detection signals in combination. Table 1 illustrates state transition when the communication terminal is turned on and then the earmicrophone is inserted into the communication terminal, and Table 2 illustrates state transition when the terminal is turned on with the earmicrophone inserted. In Table 1 and Table 2, [*, #] indicates a combination of two detection signals, with * representing a jack detection signal and # representing a switch detection signal.
TABLE 1state (1, 1)state (1, 2)beforeafterstate (1,5)earmicrophoneearmicrophonestate (1, 3)state (1, 4)earmicrophoneconnectionconnectionswitch-onswitch-offdisconnection[0, 0][1, 0][1, 1][1, 0][0, 0]
TABLE 2state (1, 6)power-on withstate (1, 5)earmicrophonestate (1, 3)state (1, 4)earmicrophoneconnectedswitch-onswitch-offdisconnection[1, 0][1, 1][1, 0][0, 0]
FIG. 6 is an equivalent circuit diagram of the jack connector illustrated in FIG. 2 during connection or disconnection of the earmicrophone jack illustrated in FIG. 1 to or from the jack connector. In the equivalent circuit diagram, the terminals 1, 4, and 5 are connected to one another.
Referring to FIG. 6, a voltage of 1.5V (=VCC×(R3/(R1+R3))=0.5×3V) is applied between the first and third resistors R1 and R3. As a result, current flows through the base of the first transistor TR1 and thus the first transistor TR1 is turned on, with a high signal output through the jack detection terminal. At the same time, current flows through the base of the second transistor TR2. That is, the transistor TR2 is turned on and a high signal is output through the switch detection terminal as illustrated in FIG. 5. In other words, since high signals are output through the two detection terminals, the controller of the communication terminal determines that a user has turned on the switch with the earmicrophone connected. In this case, the controller incorrectly senses pressing of a SEND button and thus automatically dials the latest called phone number.
FIG. 7 is a flowchart illustrating a conventional terminal operation during an earmicrophone connection. Referring to FIG. 7, the communication terminal is placed in an earmicrophone disconnection state represented as [0, 0] in step 701. This indicates that both the jack detection signal and the switch detection signal are low. When the jack is connected in step 703, the jack connector outputs a high jack detection signal and a high switch detection signal to the controller in step 705. In step 707, the controller misjudges that the switch is turned on with the earmicrophone connected by sensing the two high detection signals. While this occurs instantaneously in the process of connecting the earmicrophone, the controller performs a switch-on activated operation. That is, the controller displays the latest called phone number stored in a memory on an LCD (Liquid Crystal Display) or automatically dials the phone number as long as the switch detection signal is high in step 709.
As described above, an unintended operation such as displaying a phone number or automatically dialing occurs during an earmicrophone jack connection in the conventional communication terminal using a 4-pole earmicrophone.